First Attempt at Ha - many questions

[gnomus]

I had my first attempt with my Ha filter last night.  This gave rise to a number of new difficulties, most of which, as usual, I should have anticipated 

1) Focussing

I normally use a Bahtinov mask with 2-5 asecond exposures using SGP's 'Frame and Focus' feature.  This was interesting to say the least with the Ha filter.  There was virtually nothing on screen - attempts to lower the white level just led to noise.  I kept increasing exposure to try to see the Bahtinov spikes - I got to 40 seconds and could just make out enough in the blur to 'guess' as to where focus might be.  

Any tips for focussing when using NB filters would be much appreciated.

2) Mount

I went ahead and set up some 20 minute exposures.  Some were OK(-ish), some were just bad with ovoids where there should have been stars:

I didn't think my guiding was all that bad, but it clearly wasn't good enough.  Here is my PHD graph:

I dropped the exposures to 15 minutes, but this was giving me some White Point values that were quite low.  I still had bad frames.  All told I had to reject 4 of the 10 frames I shot (3 of 20 mins and 1 of 15 mins).  Even then I wasn't all that happy with the roundness of the stars in the frames I kept.

Any suggestions for improving my guiding?

[swag72]

Regarding your focus - If you are using a Bahtinov mask, I suggest a slew to a nice bright star (Vega for example) and in 5s exposures you will be able to see the lines. Do you use Bahtinov grabber as well? A brilliant bit of software that will nail your focus..... You'll be surprised how off you can be just eye balling it.

[michael.h.f.wilkinson]

Good first result I would say, despite having to ditch some subs

[laudropb]

A nice image for a first go.

[wuthton]

Are you using plate solving?

The integration of Plate Solve 2 in the latest version of SGP is superb. Easy to setup, fast and at everyone's favourite price, free.

[gnomus]

Are you using plate solving?

The integration of Plate Solve 2 in the latest version of SGP is superb. Easy to setup, fast and at everyone's favourite price, free.

Yes.  And I got it to work superbly last night for the first time.  I put in an AstroBin image of the veil.  It solved this.  I slewed to the co-ordinates and then centred - which was very quick (much quicker and much more accurate than my mount's alignment).  Furthermore, the meridian flip worked really well, and of course automatically re-centred the image after the flip.

I am quite new to SGP and am still discovering all of it's features.  Last night's successes with plate solving and meridian flipping were very rewarding.  It's just a pity about the guiding performance!    

[gnomus]

Regarding your focus - If you are using a Bahtinov mask, I suggest a slew to a nice bright star (Vega for example) and in 5s exposures you will be able to see the lines. Do you use Bahtinov grabber as well? A brilliant bit of software that will nail your focus..... You'll be surprised how off you can be just eye balling it.

It is brilliant. Thank you for reminding me about this. I tried using this in APT's Live View window when I was imaging with a DSLR. I never did get to grips with it. With the CCD camera, though, it was excellent.

[StargeezerTim]

Nice Eastern Veil. Can't really help with guiding, I am having a few problems myself! I use the MGEN autoguider and I upped the guidecam exposure to a second last night and that made a big difference compared to my last outing where I had to bin all my subs (luckily only 4 X 10 mins but annoying all the same).

Tim.

Edit. Meant to say... plus one for vega...  if you can't focus with that, it will have to be the moon! Lol.

[ollypenrice]

Are you using the Astrodon 3 Nm Ha filter? If so I feel your pain. A real swine to focus. Very rarely is there a star in the field on which you can focus. You have to slew away - and if you do this try to find a star at a similar altitude because the atmosphere wreaks its havoc and varies with elevation.

I suppose I ought to try Bahtinov Grabber but I'm a bit wary of software solutions I don't understand because they are brilliant at giving me numbers - but do I believe them? On the other hand, is Sara regularly out of focus? No. Is she ever out of focus? No. I think I may need to address my morbid fear of software solutions...

Olly

[gnomus]

Are you using the Astrodon 3 Nm Ha filter? If so I feel your pain. A real swine to focus. Very rarely is there a star in the field on which you can focus. You have to slew away - and if you do this try to find a star at a similar altitude because the atmosphere wreaks its havoc and varies with elevation.

I suppose I ought to try Bahtinov Grabber but I'm a bit wary of software solutions I don't understand because they are brilliant at giving me numbers - but do I believe them? On the other hand, is Sara regularly out of focus? No. Is she ever out of focus? No. I think I may need to address my morbid fear of software solutions...

Olly

I can't afford the Astrodon filters, I'm saving up for a trip to Lat 44.19 ..... and a Mesu (or possibly an Avalon) ... and then a ... and then ....

So for now I am a Baader 7 man. Sara's tip about Vega soon got me sorted. Bahtinov grabber couldn't be easier. It's click on the centre of the star and drag out a box. The numbers seemed to correspond with the visual appearance. I just need to get my d**n guiding sorted out and, increasingly, an expensive solution is emerging...... Help!

[ChrisLX200]

I use 15sec exposures with SGP and 3nM Ha filter, autofocuses just fine (@ f/5.2 anyway).

ChrisH